The present invention relates to a structure for mounting magnetoresistive elements and bias magnets in a magnetoresistive detector, wherein the magnetoresistive elements are used.
A magnetoresistive detector according to the prior art is constructed by combining a detection mechanism portion as shown in FIG. 6 and detection circuits as shown in FIG. 8.
FIG. 6 shows a perspective view of the detection mechanism portion of the magnetoresistive detector, wherein two signals, which are rectangular wave signals each having one pulse per revolution and have a phase difference of 90xc2x0 , can be obtained. Bias magnet 2 is fixed on the surface of printed circuit board 4 and on the reverse side of the printed circuit board 4, magnetoresistive elements 11, 12, 13, and 14 (indicated by the dotted lines) are fixed. A moving magnet 3 which changes a magnetic field has a detection mechanism which revolves opposite to the magnetoresistive elements 11, 12, 13, and 14.
FIG. 7 is a sectional view showing the positional relationship for mounting the respective components. 15 denotes lead portions of the magnetoresistive elements 11, 12, 13, and 14.
In FIG. 7, the magnet for changing magnetic field 3 and magnetoresistive elements 11, 12, 13, and 14 are faced with a predetermined gap therebetween, the lead portions 15 of the four magnetoresistive elements are fixed to the mountable components using the printed circuit board 4 by soldering. On the other-side surface across the printed circuit board 4, an annular bias magnet 2 is fixed. The annular bias magnet 2 is composed in that, by providing the magnetoresistive elements 11, 12, 13, and 14 with a necessary bias magnetic field, rectangular wave signals 72 and 73 each having one pulse per revolution can be obtained in the detection circuits shown in FIG. 8. Rectangular wave signals 72 and 73 each having one pulse electrically have a phase difference of 90xc2x0 therebetween and detecting such phase difference enables detection of the revolving direction.
FIG. 8 is a view showing a circuit composition of detection circuits 7.
The changes in the magnetic field produced by revolution of the magnet for changing magnetic field 3 are detected by the four magnetoresistive elements 11, 12, 13, and 14 which are faced, and then, the rectangular wave signals 72 and 73 are obtained in the detection circuits 7. R denotes resistance and VR denotes variable resistance. 71 denotes operational amplifiers which serve to wave-shape signals of the magnetoresistive elements 11, 12, 13, and 14 into rectangular waves.
In FIG. 8, since the revolving directions can also be detected, two detection circuits 7 are used.
Voltage is impressed on both ends of the magnetoresistive elements, the vector sum of the changes in the magnetic field changed due to revolution of the magnet for changing a magnetic field 3 and changes in magnetism of the bias magnet 2 is detected by the magnetoresistive elements, the detected signal voltages generated at the middle point terminals B of the magnetoresistive elements are wave-shaped by the operational amplifiers 71, whereby, the rectangular signals 72 and 73 are obtained.
Furthermore, the circuits are also constructed so that, for the purpose of eliminating effects of external noise, changes in voltage, and changes in temperature, the magnetoresistive element 11 and magnetoresistive element 13, and the magnetoresistive element 12 and magnetoresistive element 14 are combined, wherein electrical signals having a phase difference of 180xc2x0 can be obtained, and the differential signals detected by the respective magnetoresistive elements are wave-shaped.
FIG. 9 is a view showing the detailed interior composition of one magnetoresistive element. (Reference numerals 11-14 and 11A-14A are omitted for clarity.)
The magnetoresistive elements 11, 12, 13, and 14 comprise magnetoresistive detector elements 11A, 12A, 13A, and 14A (shown below in FIG. 10) and lead portions 15 (shown in FIG. 7) of the magnetoresistive elements. In a magnetoresistive element main body, tip 10 composed of two comb-shaped magnetoresistive patterns is used and C1 indicates the center of the tip 10. A, B, and C denote terminal names of lead portions 15 and the detected signals are outputted from the terminals B.
FIG. 10 is a view showing a positional relationship between the magnetoresistive elements 11, 12, 13, and 14 and annular bias magnet 2.
The centers C1 of the tips 10 of the magnetoresistive detector elements 11A, 12B, 13A, and 14A and boundary portions between N pole and S pole of the annular bias magnet 2 are positioned so as to coincide with each other. The annular bias magnet 2 is fixed on the opposite-side surface across the printed circuit board 4 and on the circumference identical to the magnetoresistive elements 11, 12, 13, and 14.
FIG. 11 is a plan showing the magnetic polarity composition of N poles and S poles of the magnet for changing a magnetic field 3 used in the prior art. The magnetoresistive elements have properties to detect magnetic changes at the magnetic boundaries between N pole and S pole, and therefore, unless the bias magnets are used, rectangular signals each having two pulses are detected per revolution.
Herein, in order to obtain one pulse per revolution, the magnetic polarity composition of the magnet for changing a magnetic field 3 on the revolution side shown in FIG. 11 and magnetic composition of the bias magnets 2 on the fixing side are employed, and the vector sum of magnetic changes according to this combination is detected, and thus, the rectangular wave signals 72 and 73 each having one pulse can be obtained per revolution.
On the other hand, according to the prior art, when the annular bias magnet 2 is positioned and fixed on the opposite-side surface across the printed circuit board 4 and on the identical circumference in alignment with the centers C1 of the tips 10 of the magnetoresistive elements and fixed printed circuit board 4, because the annular bias magnet 2 has no positioning function in the circumferential direction, and in addition, the magnetic pole position of the annular bias magnet 2 cannot be visually recognized, it is necessary to mount the annular bias magnet 2 by using positioning jigs (not illustrated).
In addition, due to the annular bias magnet 2, the other components cannot be mounted on the identical circumference on the opposite-side surface, on which the magnetoresistive elements 11, 12, 13, and 14 are not arranged, of the printed circuit board 4, and therefore, mounting density of components is lowered, and resultantly, there are problems in that the dimensions of the outward form of the printed circuit board is increased and the magnetoresistive detector cannot be reduced in size.
Therefore, the present invention aims to provide a magnetoresistive detector, wherein the bias magnet 2 can be mounted without using positioning jigs, and besides, an error in mounting the bias magnets 2 can be prevented and mounting density of components on the printed circuit board is increased, and whereby, the detector is enhanced in quality and reduced in size.
In order to solve the above problems, according to the present invention, a magnetoresistive detector is comprised of a printed circuit board, magnetoresistive elements, bias magnets, a magnet for moving magnetic field, and detection circuits for wave-shaping the signals detected by the magnetoresistive elements, wherein
said bias magnets have approximately the same dimensions of the magnetoresistive elements and are fixed so as to overlap the magnetoresistive elements, and on the printed circuit board, holes, having approximately the same dimensions of the magnetoresistive elements, for positioning and fixing the magnetoresistive elements are disposed.
Furthermore, two types of the bias magnets are provided, the outward form of the two types of bias magnets are different from each other, two types of outward form of the holes of the printed circuit board which are corresponded to the outward forms of the two types of bias magnets are provided, and marking lines for recognizing the boundaries of magnetic poles are provided on the surfaces of the bias magnets.
Moreover, said bias magnets are provided with mis-mounting prevention portions and are provided with marks for recognizing the boundaries of magnetic poles.